A partially open firebox of a fireplace (hearth) as well as a firebox (furnace) closed except for the air supply are utilized in residences and are to contribute toward a cozy room atmosphere, particularly on cold and humid days. Approximately 300-500 m.sup.3 of room air per hour are required for the flawless operation of an open fireplace in a residence. The air is supplied, inter alia, through cracks in windows and doors. Since here the air supply is frequently inadequate, smoke can enter the living space.
In a conventional improved arrangement, the required air is supplied through a partially open basement window and a floor aperture in the immediate vicinity of the firebox. As a result, the basement becomes colder; the window must be screened in order to prevent animals (mice, rats, martens, cats) from entering the basement.
In another known system, the flue of the fireplace is located in the direct proximity to an outer building wall wherein an opening is provided. Air is taken in through this opening on account of the hot flue gases exiting the room via the chimney. The taken in air is frequently conducted, for warming up purposes, through a heat exchanger heated by the hot flue gases or by the radiant heat from the burning material. This conventional air supply unit operates satisfactorily with respect to the amount of air supplied and the heating of the latter; however, the installation site for the open firebox is linked to the proximity of an outer wall of the building.